Wiley Pathways Personal Computer Hardware Essentials - Softcover

Groth, David; Gilster, Ron

Softcover

ISBN 10: 0470074000 ISBN 13: 9780470074008

Publisher: Wiley, 2008

Synopsis

From multicore CPUs and SATA hard drives to PCIe expansion buses and peripherals, this text offers practical and concise explanations of contemporary and popular PC hardware. Along with detailed coverage of essential A+ hardware topics, students will find an indispensable guide to building, maintaining, upgrading, and troubleshooting desktop computers and laptops.

Packaged Set (Text + PC Hardware Essentials Project Manual): 0470-221089

About this title

About the Author

David Groth is a full-time author and consultant. He is the author of the Sybex's bestselling Network+ Study Guide as well as I-Net+ Study Guide and Cabling: The Complete Guide to Network Wiring. Groth holds many technical certifications, including A+, Network+, Server+, Security+, MCSE, and CNI.

Ron Gilster (CCNA, CCSE, i-Net+, Network+, A+, MBA, and AAGG) has been involved with Cisco networking and internetworking since 1993 as a trainer, teacher, developer, merchant, and end user. He has more than 35 years of total computing experience, including more than 15 years involved with the networking of computers. He also has extensive experience consulting in computer-related areas, including working on mainframes, minicomputers, and virtually every type of personal computer and operating system that exists. He has held consulting and management positions with several high profile companies. Ron is semi-retired, writing and teaching the occasional college course. He is the author of CCDA For Dummies, Cisco Networking For Dummies, A+ Certification For Dummies, Network+ Certification For Dummies, Server+ Certification For Dummies, and i-Net+ Certification For Dummies, plus several books on networking, including wireless networking, the Internet, computer hardware, computer and information literacy, and programming.

Megan Miller is an editor and writer with 20 years experience in publishing, technical project management, and interactive communications.

Excerpt. © Reprinted by permission. All rights reserved.

Wiley Pathways PC Hardware Essentials

By David Groth Ron Gilster Megan Miller

John Wiley & Sons

Copyright © 2007 David Groth
All right reserved.
ISBN: 978-0-470-07400-8

Chapter One

HARD DRIVES

Starting Point

Go to www.wiley.com/college/groth to assess your knowledge of hard drives.

Determine where you need to concentrate your effort.

What You'll Learn in This Chapter

* The components and characteristics of hard drives and how they work

* PATA and SATA standards for hard drives and how to install and configure an ATA hard drive

* SCSI standards for hard drives and how to install a SCSI hard drive

* Hard drive partitioning, formatting, and management

After Studying This Chapter, You'll Be Able To

* Compare hard drives in terms of industry standard ratings

* Identify recent hard drive standards

* Distinguish unique installation considerations for different hard drive technologies

* Choose an appropriate hard drive and interface for an existing PC Determine partitioning and formatting limits and options for a given operating system

* Install, partition, and format a hard drive

* Use system utilities to review the status of a hard drive

* Troubleshoot a faulty hard drive

INTRODUCTION

The system memory that is used by the PC to temporarily store data coming from and going to the CPU is often referred to as primary storage. In addition to system memory, PCs also need permanent, nonvolatile storage areas for larger amounts of data. Nonvolatile means that the data stored on a component is not lost when power to the component is turned off. These nonvolatile storage components are often referred to as secondary storage. Today, the most common secondary storage components are hard drives, and these typically store the bulk of the data that a PC uses. This data includes not just user documents and files, but also user and system software, such as Microsoft Word and Microsoft Office, and any files and data needed to support running these applications. Hard drives typically reside inside the computer (although there are external and removable hard drives) and can hold more information than other forms of storage.

7.1 Understanding How Hard Drives Work

One of the most common upgrades to a PC is adding or replacing a hard drive in order to gain more storage space. To choose a compatible drive for your system, it is important to understand a few of the basics of hard drives and how they work. Understanding the main characteristics of hard drives and how hard drives are rated will also help you compare equivalent hard drives from different manufacturers and select the one that is right for your needs.

7.1.1 Hard Drive Components

Hard drives, also called hard disk drives, hard disks, or fixed disks, consist of several small, identical disks called platters stacked together and placed in a sealed enclosure to protect them from dust or damage. The platters are made of aluminum or glass, and are coated with a thin layer of magnetic media that stores the actual data.

The platters are mounted through their centers on a small rod called a spindle. The disks are rotated about the spindle at a speed typically between 4,500 and 15,000 revolutions per minute (RPM). As they rotate, read/write heads float approximately 10 micro inches (about one-tenth the width of a human hair) above the disk surfaces and make, modify, or sense changes in the magnetic positions of the coatings on the disks. Read/write heads have sensors and magnets used for reading and writing magnetic charges on the platters' surfaces. The read/write heads are connected to an actuator arm, which is used to precisely position the heads over the correct area on the platters (Figure 7-1).

Hard drives also contain a logic board that contains the circuits and chips that control the drive's performance. The disk controller is the main circuit on the logic board that controls everything from handling requests for data to managing the mechanics of the motor, actuator arm, and read/write heads.

Also essential to the functioning of a hard drive is the host adapter, or host bus adapter (HBA), logical circuitry that physically connects the hard drive to the "host"-the PC. The host adapter handles basic input/output processing, converting signals from the hard drive controller to signals the PC can understand. The host adapter may be an expansion card plugged into the motherboard or its circuitry may be built directly into the motherboard.

Hard drives come in several sizes. Older hard drives were designed to fit 5.25 inch drive bays but most modern desktop computer hard drives today are designed to fit in the standard 3.5 inch drive bays. Older hard drives were much taller than modern drives and are called "full-height." Modern drives are shorter, "half-height" or even slimmer. Inside the PC, internal hard drives are connected by cables to the power supply and to the host adapter.

7.1.2 Drive Geometry

To read and write data to the magnetic platters of a hard drive, the drive is electronically organized into sections recognized by systems software. This organization is called drive geometry. The components of a hard drive's physical geometry include:

* Heads: A hard drive usually has one read/write head for each surface of a platter; a drive with four platters has eight read/write heads.

* Tracks: Data is written to and read from the surfaces in concentric rings called tracks. The rings, or tracks, are numbered from the outside track in, with the outside track given the initial number 0. The total number of tracks that a surface can have depends on the drive's engineering; today's hard drives may have over 16,000 tracks on each surface.

* Cylinders: Because all heads are on a single actuator arm, the heads read the same track number on each surface at the same time. If the actuator arm moves to Track 12, all heads will be reading from Track 12 on the separate surfaces. The collection of tracks at a single actuator-arm position is known as a cylinder (Figure 7-2). The total number of tracks per surface is the same as the number of cylinders. In fact, the disks' tracks aren't treated as individual tracks on single disks; they're treated as cylinders, and manufacturers more commonly note the number of cylinders that a drive has. If you need to know the number of total tracks a hard drive has over all surfaces, you can multiply the number of heads by the number of cylinders.

* Sectors: To organize and locate separate chunks of data on a surface, the platter is divided into 60 or more wedges that divide short sections of tracks into smaller segments called sectors. Sectors are the smallest accessible portion of data on a track, and all sectors, regardless of their physical size, are defined as holding 512 bytes of data. When information is read from or written to a drive, the heads read or write a sector-sized division of a cylinder, from top surfaces to the bottom. In this physical geometry, with sectors defined by wedges, a certain amount of waste is built in: The sectors at the outer edges are physically quite a bit larger than inner sectors. To fit more sectors in to the outer tracks, zone bit recording (ZBR), or multiple zone recording was built in (Figure 7-3). ZBR divides the platters into different zones, nearer and further away from the spindle, and sectors within these zones are given a specified number of sectors per track. This allows outer tracks to have more sectors.

The PC's BIOS, however, is programmed to access each block of data through CHS (cylinder, head, sector) addressing and is unable to work with ZBR. To accommodate the needs of ZBR, drives were designed to have a logical geometry that was different from their physical geometry. The drive is given theoretical CHS values, which approximate the drive's total storage space. These values are its logical geometry and the hard drive controller uses these values to communicate with the BIOS. The drive itself is engineered to work with actual physical geometry (which can use ZBR) and can translate to and from the logical values needed by the BIOS using sector translation.

Sector translation uses a translation table that converts the actual physical geometry of a drive into the logical geometry used by the BIOS. An older method of sector translation, extended CHS (ECHS), uses logical values based on the traditional divisions of cylinders, sectors, and heads. Today, more drives use logical block addressing (LBA), which numbers all sectors on a drive sequentially, without reference to cylinders and heads.

7.1.3 Hard Drive Characteristics

There are a variety of characteristics and statistics that are used to rate and compare hard drives, including:

* Capacity: The capacity or size of a hard drive refers to how many bytes of data the drive can store. Capacity is determined by drive geometry. Each sector can contain 512 bytes, and a track can contain up to 63 sectors, so the total storage space of a hard drive can be determined by the following formula:

Capacity = 512 Bytes per sector x 63 Sectors per track x Cylinders x Heads

Typical PC hard drives today have capacities ranging from 40GB to 500GB and higher.

* Spin speed: The spin speed is how fast the platters are spinning, measured in revolutions per minute (RPM). Higher RPM values mean faster speeds and faster access to data. Depending on the model, disks today typically rotate between 4,500 RPM and 15,000 RPM.

* Seek time: Seek time is the time it takes for the read/write head to react to a request and position itself over a track. A seek from one track to the next (called a track-to-track seek) is usually quickest; a seek from the innermost to the outermost track (called a maximum, or full stroke seek) is longer. The average seek time is usually defined as the time it takes the head to move one-third of the way across the platter, which typically takes from 5 to 10 ms.

* Rotational latency: Rotational latency is the time it takes for a requested sector to travel to the head after the read/write head is in position, and is measured in milliseconds. Rotational latency is determined by the spin speed (RPM). Average rotational latency is the time it takes for a disk to turn 180, and can be determined by the following formula:

Average Rotational Latency = (60)/(2 x RPM) x 1000.

The worst-case latency is the time for the disk to make a full revolution. Of the seek time and the latency period, the seek time is usually the longer wait.

* Access time: The access time measures the full amount of time that it takes to move the read/write head to the correct position and access the correct sector. The average seek time plus the average latency equals the drive's access time. The smaller the access time value, the faster the drive. The formula for access time is:

Access time = Average seek time + Average Rotational Latency

* Interface: The interface is the technology used to connect the hard drive to the rest of the system. The interface determines not only the type of physical connections and cables, but also the rate of data transfer to and from the hard drive. Interface technologies include the Advanced Technology Attachment (ATA) standards and the Small Computer Systems Interface (SCSI) standards, each of which is discussed in more detail later in this chapter.

* Disk cache size: To improve access times and data throughput, modern drives include a disk cache or buffer that may hold from 1 to 8 or more MB of data. The disk cache is used to store frequently used or recent data and helps to minimize the number of physical seeks to the hard drive.

* Data transfer rate: The data transfer rate measures the total amount of data that the drive can transfer over a specified time period, usually 1 second. The data transfer rate of a drive depends on its internal and external transfer rates. The external transfer rate measures the time taken to transfer data between the PC's RAM and the drive's disk cache. The internal data transfer rate measures how fast the drive can move data between its disk cache and the platter surface.

* Data transfer mode: The data transfer mode is the protocol used to transfer data to and from the hard drive. The data transfer mode is prescribed by the drive interface. SCSI hard drives use SCSI data transfer modes. Early parallel ATA drives used the PIO (Programmed Input/ Output) mode, which relied on the CPU to control the transfer of data from the hard drive. The DMA (Direct Memory Access) mode relieves the CPU of this duty, and transfers data directly to RAM. DMA modes can also be grouped into two categories: single word DMA modes and multiword DMA modes. Single word DMA transfers data one word (two bytes of data or 16 bits) at a time. Multiword DMA transfers several words at a time in a kind of burst. UltraDMA (UDMA) is the most recent version of DMA and has transfer rates up to 150MBps.

7.1.4 Reading and Writing Data

During writing, the head's magnet is energized to polarize a small portion of the magnetic material. During reading, the head recognizes any flux transitions (changes from nonpolarized segments to polarized segments and vice versa) and interprets combinations of these changes as binary 1s or 0s. The process of translating from binary to flux transition patterns is called encoding. The simplest encoding method is to interpret the presence of a flux transition as a 1 and the absence as a 0. More complex methods were devised to allow for better performance on more densely packed drives. Early encoding methods included Frequency Modulation (FM), Modified Frequency Modulation (MFM), and Run Length Limited (RLL). On today's drives, PRML (Partial Response, Maximum Likelihood) and EPRML (Extended PRML) encoding methods analyze much smaller fluctuations to determine the sequence of bits. These encoding methods allow for far greater density of tracks and sectors on hard disks than previous encoding methods.

To make it easier for the operating system to manage the storage space, the information encoded on the drive is written to groups of sectors known as clusters. A cluster is made up of up to 64 sectors grouped together (the actual number of sectors included in a cluster varies with the size of the hard drive).

Traditionally, encoding utilized longitudinal recording, writing, and reading parallel to the disk surface. New technologies of perpendicular, or vertical, recording (PR) allows writing to layers below the disk's surface plane, greatly increasing storage capacities.

None of these encoding methods are 100 percent perfect-all data transmission technologies will experience some very small rates of error. Data errors can also be caused by the magnetic fields fading over long periods of time. Hard drives are designed with error correction mechanisms to recognize errors and correct them during transmission. Essentially, error correction methods use the hard drive controller to write extra bits of data, called the error correction code (ECC) wherever it writes a segment of data to the disk. When that same data is read, the ECC is analyzed to see if any errors have crept into the data.

7.2 Understanding and Installing ATA Hard Drives

Early PCs needed separate controller cards attached to the motherboard to connect the drive to the computer and manage transfers. Later PCs improved on this technology with the development of integrated device electronics (IDE) drives that had embedded controller circuitry into the drives themselves. A succession of standards, known as the ATA (Advanced Technology Attachment) standards, specified how early IDE and later hard drives interfaced with the PC. The first ATA standards used a parallel bus, transferring 8 bits at a time, and are called parallel ATA (PATA). Recent ATA standards specify the use of a faster, serial bus and are called serial ATA (SATA).

(Continues...)

Excerpted from Wiley Pathways PC Hardware Essentialsby David Groth Ron Gilster Megan Miller Copyright © 2007 by David Groth. Excerpted by permission.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
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Edition details

• Publisher: Wiley
• Publication date: 2008
• Language: English
• ISBN 10: 0470074000
• ISBN 13: 9780470074008
• Binding: Paperback
• Edition number: 1
• Number of pages: 548